The move came one day after KT warned it will restrict access of Internet-connected TV applications to its network, claiming they "free-ride" on its network. Such free-riding can cause heavy cyber traffic, slowing other users' access to the Internet.

KT and other fixed-line operators have requested smart TV producers pay money in return for using its Internet network since last June.

KT said its move will only affect Samsung's smart TVs. The company is currently in talks with LG Electronics over payment for network usage.

"Since Samsung said it will not negotiate, we have decided to restrict access of its smart TV applications to our Internet networks," KT said in a statement.

KT's push may hurt efforts by Samsung Electronics, the world's No. 1 TV maker, to increase sales of Internet-enabled TVs in the face of a general global economic slowdown that is denting sales of traditional sets.

Samsung Electronics is aiming to sell at least 25 million units of smart TVs this year. According to market watchers, domestic sales of smart TVs could reach around 1 million units.

Samsung said it will take legal actions against KT's unilateral move, saying that the action hurts customers' right to non-discriminately use the network.

The country's telecommunications watchdog on Thursday called KT's move "inappropriate," saying that it may punish the company if the move violates related laws.

"If KT maintains its stance, the watchdog plans to take every measure to protect customers' rights," the Korea Communications Commission said in a statement.